Biramous in the context of "Crustaceans"

Crustaceans (from Latin word "crustacea" meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (/krəˈsteɪʃə/), a large, diverse group of mainly aquatic arthropods including the more familiar decapods (shrimps, prawns, crabs, lobsters and crayfish), seed shrimps, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, opossum shrimps, amphipods and mantis shrimp. The crustacean group can be treated as a subphylum under the clade Mandibulata. It is now well accepted that the hexapods (insects and entognathans) emerged deep in the crustacean group, with the completed pan-group referred to as Pancrustacea. The three classes Cephalocarida, Branchiopoda and Remipedia are more closely related to the hexapods than they are to any of the other crustaceans (oligostracans and multicrustaceans).

The 67,000 described species range in size from Stygotantulus stocki at 0.1 mm (0.004 in), to the Japanese spider crab with a leg span of up to 3.8 m (12.5 ft) and a mass of 20 kg (44 lb). Like other arthropods, crustaceans have an exoskeleton, which they moult to grow. They are distinguished from other groups of arthropods, such as insects, myriapods and chelicerates, by the possession of biramous (two-parted) limbs, and by their larval forms, such as the nauplius stage of branchiopods and copepods.

A shrimp (pl.: shrimp (US) or shrimps (UK)) is a common name typically used for crustaceans with an elongated body and a primarily swimming mode of locomotion – usually decapods belonging to the Caridea or Dendrobranchiata, although some crustaceans outside of this order are also referred to as "shrimp". Any small crustacean may also be referred to as "shrimp", regardless of resemblance.

More narrow definitions may be restricted to Caridea, to smaller species of either of the aforementioned groups, or only the marine species. Under a broader definition, shrimp may be synonymous with prawn, covering stalk-eyed swimming crustaceans with long, narrow muscular tails (abdomens), long whiskers (antennae), and slender, biramous legs. They swim forward by paddling the swimmerets on the underside of their abdomens, although their escape response is typically repeated flicks with the tail, driving them backwards very quickly ("lobstering"). Crabs and lobsters have strong walking legs, whereas shrimp typically have thin, fragile legs which they use primarily for perching.